1. Field of the Invention
The present invention relates to a method and an apparatus for drying flat objects, particularly semiconductor wafers such as silicon wafers.
2. Description of the Related Art
In a process of manufacturing flat objects, such as lenses, optical discs, liquid crystal panels, solar cells, silicon wafers, and wafers of compound semiconductors such as GaAs compound semiconductor, GaP compound semiconductor, and InP compound semiconductor, the flat objects are cleaned and then dried. Conventionally, such flat objects are dried through use of one or more of the following methods: a method in which flat objects are exposed to a vapor of an organic solvent such as isopropyl alcohol (IPA) to thereby be dried through replacement of water present thereon with the organic solvent (IPA drying or the like); a method in which flat objects placed in a carrier are subjected to a centrifugal force to centrifugally remove adhering water, thereby drying the flat objects (spin drying); a method in which flat objects are subjected to heat from a heat source such as a halogen lamp to thereby be dried through evaporation of water (IR drying); a method in which flat objects are immersed in hot pure water and are then gradually pulled up to thereby be dried through utilization of surface tension of pure water (drying through pull-up from hot water; see Japanese Patent Publication (kokoku) No. 6-93449); and a method in which flat objects are placed in a sealed drying container, and the container is evacuated under reduced pressure to thereby dry the flat objects through removal of evaporating water (drying under reduced pressure).
However, these conventional drying methods involve the following problems. Drying through use of an organic solvent such as IPA drying involves a potential danger of explosion or fire due to volatility of an organic solvent, and thus safety is endangered. In spin drying through utilization of a centrifugal force, cleanliness of flat objects may be impaired due to particle generation induced by contact between flat objects and a carrier and from a revolving drive component during rotation thereof. In IR drying with a halogen lamp or a like heat source, flat objects can in principle only be dried one by one, resulting in relatively low productivity. In drying through pull-up from hot water utilizing surface tension of water, flat objects must be pulled up very slowly from hot water, resulting in significantly low productivity. In drying under reduced pressure through evacuation of a container under reduced pressure, there arises a problem that water is condensed due to removal of heat of gasification.